To keep a rigid control over the cooling, therefore, a
thermostat valve is used, which automatically keeps the cooling water
temperature at a predetermined value. The thermostat is used in engine cooling
systems and it is used to maintain a system’s temperature.
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Bellows type
Wax or hydrostatic type
Bellows type thermostat
It consists of
metallic bellows filled with some volatile liquid like acetone. The valve is
fitted in the water hose pipe at the engine outlet. When the engine after starting is warming up, it is desired that the cooling system should not operate so that
the engine warms up early. During this period, the thermostat valve remains,
closed, because the liquid inside as yet has not changed its state and, therefore,
does not exert exert any pressure on the valve.
But as the cooling water temperature
reaches a predetermined value, 75-80oc the liquid inside is
converted into vapour which exerts pressure on the valve, which begins to
open, so that the water circulation starts. The valve then opens gradually further
as the water temperature rises, until it is fully open at about 90-95oc.
Thus the thermostat controls the flow of water through the radiator according
to the engine cooling requirements.
Wax
thermostat
As the coolant is heated, it transmits
its heat to the copper-loaded wax having a high coefficient of thermal expansion
which expands so that the rubber plug contracts against the plunger and exerts
a force on it upwards so that it moves vertically. This movement of the plunger
opens a valve in the thermostat to allow coolant to flow through the radiator.
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